The present invention relates in general to the energy management of a multiplicity of energy conversion units which together supply load upon demand to a given process through a common junction, and more particularly to a system which economically optimizes the load distribution among the multiple units dynamically during the transition of process load demand from one state to another such that when the process load supply reaches the other process demand state, the energy conversion units are substantially in their economically optimum individual load generating states.
Typical unit load dispatching plants may include a boiler house in which a multiplicity of boilers are coupled to a common header for supplying steam flow to the particular process, a power turbogeneration system in which a multiplicity of turbogenerating units supply power to a power system network through a common bus, and a heat exchange industrial process in which a multiplicity of power-driven compressors are used together with corresponding chiller units for maintaining the temperature of a common coolant under varying coolant flow demand conditions, for example. In each case, the total load demand of the process is supplied cooperatively and coordinately by the individual energy conversion units used for the particular application. By optimizing the energy conversion units for equal incremental cost unit load supply to yield the process demand load, a substantial cost savings can be achieved.
Typical state of the art optimizing procedures and control systems for economic load allocation of a multiplicity of load generating units for a given steady state total load demand of the process are described in the following papers:
(1) "Optimization of Non-Linear Power Plant Systems" by R. E. J. Putman, published in Proc. IASTED Conf., pages 1-6, June, 1978;
(2) "Optimal Boiler Load Allocation in Distributed Control" by T. N. Matsko et al., published in Proc. American Control Conf., pages 1140-1145, June, 1982.
While the optimizing systems of the aforementioned types do provide one or more methods for economic unit load dispatching of a multiplicity of energy conversion units, they propose to do so solely at steady state process load demand conditions. In other words, the optimization procedure is relaxed or suspended during load demand transitions. As described in the Matsko paper referenced above, all of the energy generating units are moved in load supply according to the change in process load to satisfy the process demand, then a separate reallocation is effected to equalize the incremental load costs among the individual load supply units while maintaining the total steady-state load demand. Accordingly, such control systems separate the demand control from the optimal reallocation procedure for the transient and steady-state conditions.
In those cases in which the energy generating units are moved unnecessarily in trying to support the load during the process load transition and then are moved again at the final steady-state condition according to a reallocation in unit load to equalize the incremental load costs among the individual units, the result is an undesirable waste of fuel in having to govern the energy generating units through the unnecessary load transitions, not to minimize the effects of wear and tear on the units themselves in being operated through such transitions.
Clearly, it would be economically advantageous to avoid this unnecessary waste of fuel by determining before-hand which boilers should be altered in unit load supply and in what direction to achieve the optimum economic unit load distribution for a process load demand transition. It is understood that according to their individual efficiency characteristics, some load supply units may be increased in load, some decreased in load and some may not be required to alter their load supply at all in order to achieve the optimum economic unit load distribution in the transition from one process load demand to another. The present invention proposes a system which is operative to make judgments as to how to operate the individual units collectively during a process load transition as well as at steady-state to achieve the aforementioned desired result.